P1870 on GMC
Transmission Component Slipping
P1870 on GMC vehicles indicates transmission component slipping. Au7o has documented this code across 1 GMC model — most commonly on Sierra 1500. This manufacturer-specific code (common on GM and Ford automatics, e.g. 4L60E) means the computer detected slippage between transmission components, most often at the torque converter clutch, where commanded engagement does not match actual behavior. When it sets, the PCM typically raises line pressure to protect the transmission and may lock out the converter clutch. Symptoms include harsh or delayed shifts, RPM flare/slipping, and reduced fuel economy. It often points to a worn valve body bore or TCC components and should be addressed before further internal damage occurs. Typical repair costs on GMC range from $1,800 to $3,500, depending on the specific model and root cause.
Common Causes of P1870
- •Worn torque converter clutch (TCC) regulator valve bore in the valve body
- •Faulty TCC solenoid or PWM solenoid
- •Worn or failing torque converter clutch
- •Low or degraded transmission fluid
- •Worn internal clutches or seals (e.g., input shaft O-ring)
- •Worn valve body / internal hydraulic leak
P1870 on GMC by Model
GMC Sierra 1500(1 issue)
- 4L60-E / 4L65-E Sun Shell Failure Causing Loss of Reverse and 2nd/4th Gear2000-2007
On GMT800 Sierra 1500 trucks equipped with the 4L60-E family automatic, a well-known internal failure is cracking or stripping of the reaction sun shell. Owners commonly report sudden loss of reverse, no 2nd gear, no 4th gear, or a truck that starts in 3rd gear after a bang or flare. This is widely documented in transmission rebuild literature, repair databases, and owner reports for GM trucks and SUVs using this transmission.
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View P1870 across all makes →Frequently Asked Questions
What does P1870 mean on GMC?▼
P1870 stands for "Transmission Component Slipping." This manufacturer-specific code (common on GM and Ford automatics, e.g. 4L60E) means the computer detected slippage between transmission components, most often at the torque converter clutch, where commanded engagement does not match actual behavior. When it sets, the PCM typically raises line pressure to protect the transmission and may lock out the converter clutch. Symptoms include harsh or delayed shifts, RPM flare/slipping, and reduced fuel economy. It often points to a worn valve body bore or TCC components and should be addressed before further internal damage occurs. On GMC specifically, this code is documented across 1 model.
What causes P1870 on GMC vehicles?▼
Common causes on GMC: Worn torque converter clutch (TCC) regulator valve bore in the valve body, Faulty TCC solenoid or PWM solenoid, Worn or failing torque converter clutch, Low or degraded transmission fluid, Worn internal clutches or seals (e.g., input shaft O-ring). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P1870 on a GMC?▼
Repair costs on GMC range from $1,800 to $3,500, depending on the specific model and root cause.
Which GMC models have P1870 documented?▼
Au7o has documented P1870 on 1 GMC model: Sierra 1500.